This invention is directed to a lock gate blade type valve and more particularly to a lock gate valve for particulate or flowable bulk-type material having curved blades for controlling the flow through a conduit.
My prior patents illustrate lock gate flow control or metering valves for flowable bulk material which control the flow with a pair of curved flow control blades. Thus, my U.S. Pat. Nos. 3,813,015; 3,556,358 and 3,799,187 shows lock gate valves in which the top and bottom blades are reversed in relative position to each other such that the material entering the valve falls on a convex surface of the upper blade. When the upper blade opens, the material passes into a valve holding chamber and falls onto a concave surface of the lower blade. My patents also show arrangements for sealing the moving blades along the moving surfaces, and my U.S. Pat. Nos. 3,556,358 and 3,813,015 illustrate pneumatic control systems for causing and controlling the sequential movement of the blades and blade arms.
Many lock gate valve installations have a requirement for enclosing the working components of the valve for the control of the flow of dry particulate material. Fully enclosed lock gate valves, that is, valves in which the blade arm and blade mounting and moving mechanisms are enclosed, are desirable for preventing the possibility of contamination by the leakage of material outside the valve to the material inside the valve, and also for preventing any leakage of the material being handled by valve to prevent contamination to the atmosphere and environment external to the valve.
A fully enclosed lock gate valve also using inverted flow control blades, as previously described, is shown in my U.S. Pat. No. 3,907,178 issued Sep. 23, 1975. Due to the necessity for providing large exterior chambers on either lateral side of the valve for housing the blade and blade arms, and due to the extent of blade movement, the valve operating cylinders, as identified by reference numerals 60 and 62 in patent '178, extended to positions above and below the respective top and bottom mounting flanges of the valve. Therefore, installation of the valve shown in my U.S. Pat. No. 3,907,178 in confined conditions was complicated when the valve could not easily be moved in and/or out of position due to the additional headroom required at the top and the bottom of the valve for the cylinders.
The lock gate valves as shown in certain of my prior patents had a disadvantage due to the fact that the bottom flow control blade was inverted with respect to the upper blade. At the time these inventions were made and the corresponding patent applications were filed, it was considered desirable that such valves have a holding chamber between the blades of maximum capacity. While I believed that a blade which curves into the direction of material flow is to be preferred over an inverted blade, for the bottom blade this provided complications in design which I had been unable to resolve. Since I considered any reduction in the measuring or holding capacity of the valve to be generally undesirable, the bottom blade was positioned in inverted relation to the top blade, even though it had a higher stress placed on it by reason of the weight of material resting thereon. The bottom blade was harder to seal, and required more power to operate, than the upper blade.
In some instances, a lock gate or flow measuring valve was made using two single bladed valves of the type shown in my U.S. Pat. No. 3,380,475 issued Apr. 30, 1968, with one valve mounted above the other in a common conduit, as illustrated in FIG. 4 of my U.S. Pat. No. 3,813,015. While this resulted in what I believed to be a superior positioning of the flow control blades, it also resulted in an unwieldy height to the overall mechanism and an added expense, both of which restricted its use.
It is often desirable to substitute a curved or rolling blade type of lock gate valve for a conventional rotary feed valve. Rotary feed valves themselves have certain advantages, but also have disadvantages in that they require substantially greater power to operate, and usually require expensive, explosion proof electric drive motors. Due to the power input requirements, they can generate a substantial amount of heat as the valve rotates. Therefore, while it may be desirable to replace a rotary valve with a more simple and energy efficient rolling blade valve, space requirements are usually strict, thereby demanding a compact rotary valve arrangement.
Automatic weighing systems now favor metering valves which dispense smaller portions or increments of bulk material and at a faster rate. Many such systems require that the material be supplied in smaller increments to provide a smoother delivery and greater accuracy in weighing and blending component parts of a mix, such as an animal feed mix. Therefore, the increased capacity which was available between the inverted blades as illustrated in my prior lock gate patents are not required or even desirable for many installations.